1. Field of the Invention
This invention relates generally to the design and manufacture of a color display system. More particularly, this invention relates to an improved design and system configuration for a virtual image color display system incorporating a color shutter assembly and off-axis optical configuration wherein the ambient reflection is greatly reduced and a magnified image in color is provided without requiring large image source or high voltage power input such that the power consumption and radiation from a color display system can be substantially reduced.
2. Description of the Prior Art
Since large size color image displays with high intensity bright colors are highly desirable in modern color display systems, such systems are often limited by the concerns that high power input is required to produce high intensity bright images thus causing high power consumption and generating higher level of radiation. Even that better quality and more pleasant images are provided by larger and brighter color display systems, concerns of health hazards for close distance long term operation may limit the application. Additionally, the `ghost image` caused by ambient reflection generated frequently from self-reflection may also interfere and adversely affect the visual performance of the display system. Even that high quality of optical performance can be achieved by display systems applying on-axis or near on-axis virtual image techniques, the undesirable effects caused by the ambient reflection with the ghost images continue to be conspicuous and visually annoying. As more color monitors and greater size television sets are being used, there are greater demands for overcoming these limitations whereby the benefits of larger, brighter and better quality image displays can be fully realized both at work place and in enjoying a wide variety of electronic entertainments.
In order to reduce the ambient reflection, one of a conventional techniques is by the a circular polarizer which reduces the reflection of the ambient light because the reverse of the handness of polarization in reflection. The reduction of ambient reflection is significant. But for a high quality color display system, particularly for the high performance system utilizing the on-axis or near on-axis virtual image techniques, the reduction is still not adequate.
Ziegler discloses in U.S. Pat. No. 4,657,348 entitled `Arrangement to Remove Reflection from Liquid Crystal Displays (LCDs)` (issued on Apr. 14, 1987) an optical arrangement to remove reflection from LCD display by employing a cover disk in front of the LCD which is disposed obliquely to and apart from the LCD. A quarter wave retarding foil is disposed on the liquid crystal cell. The cover disk includes a polarizer. The quarter wave foil cooperates with the polarizer to substantially remove the reflection fro the light passing through the cover disk. Application of the polarizer together with the .lambda./4 plate to remove the ambient reflection is thus well known in the art. However, such technique imposes several limitations for modern display devices, particularly for the virtual image color display systems. First of all, for a virtual image display, the blocking of the ambient reflection by this conventional method also reduces the brightness of the image display. It is caused by the reduction of the image reflection by the polarizer and .lambda./4 retarding foil. Additionally, for a virtual display monitor employed with computers in a office setting, there are generally strong overhead lights projecting strong ambient light to the viewing window. The ambient reflection of these overhead lights interfering with the virtual display images and becomes are very annoying.
In another U.S. Pat. No 5,278,532, entitled `Automotive Instrument virtual Image Display` issued on Jan. 11, 1994, Hegg et al. disclose a virtual image automotive instrument display system. Special shielding designs are used to prevent strong ambient reflection. Unlike automotive instrument display systems, a larger virtual image display system such as larger size televisions or computer monitors, the display images are more vulnerable to ambient reflection due to the larger size of the viewing windows and the projection of overhead lights onto the screens on the widows. The shield designs which may be effective for automotive instrument application are not adequate for modern larger size display apparatuses.
In the art of designing and manufacturing virtual image color display systems, a need still exists for a novel system configuration and design method to more effective remove the ambient reflection. Particularly, for a color display system such as a computer monitor, where an operator often sits many hours underneath strong overhead lights, there is an urgent need to provide a novel color display system which can provide bright color image display without high level of radiations while reducing the interferences from the ambient reflection and reflection from the strong overhead lights to a minimum amount.